Page 196 - Boiler plant and distribution system optimization manual

Chapter 11

Boiler Plant Calculations

FINDING ExCESS AIR USING FLUE tionship for excess air for oxygen levels
GAS ANALYSIS OF CARBON DIOxIDE (CO ) between 0% and 4%. See Table 11-1.
2
AND OxYGEN (O ) (Ans .: Multiply oxygen by 5 to get excess
2
air or divide excess air by 5 to get oxygen)
The purpose of this section is to demonstrate
how to find excess air when either the carbon di- 5. Why is the maximum CO level at 0% ex-
2
oxide (CO ) or oxygen (O ) content of the com- cess air higher for no. 6 fuel oil than for
2 2
bustion products is known. Natural Gas? See Tables 11-1 and 11-2.
The use of a greater amount of combustion (Ans.: There is more carbon in heavier
air than is necessary constitutes a major waste of fuels.)
energy. Measuring the excess air of a combustion
process is necessary to control this loss.
USING CARBON
Explanation: DIOxIDE (CO ) MEASUREMENTS
2
a. In the Combustion Tables find the table for
the fuel being fired. 1. Find the excess air when firing natural gas
for a carbon dioxide (CO ) level of 10%. See
2
b. In the three left hand columns, find either Table 11-1.
the carbon dioxide or oxygen content of the (Ans.: 14.8%)
combustion products and read the corre-
sponding excess air level. 2. Find the excess air when firing no. 2 fuel oil
for a carbon dioxide (CO ) level of 15%. See
2
1. The measured oxygen level in a natural Table 11-3.
gas boiler is 8%, what is the excess air? (Ans.: 4.6%)
See Table 11-1.
(Ans.: 54%) 3. Find the excess air when firing no. 6 fuel oil
for a carbon dioxide (CO ) level of 15.5%. See
2
2. The measured CO level for a boiler Table 11-1.
2
burning natural gas is 9%, what is the ex- (Ans.: 7.2%)
cess air? See Table 11-1.
(Ans.: 28%)
USING OxYGEN MEASUREMENTS
3. The measured CO level for a boiler
2
burning No. 6 fuel oil is 15%, what is the 1. Find the excess air when firing natural gas
excess air? See Table 11-2. for an oxygen (O ) level of 10%. See Table 11-
2
(Ans.: 10%) 1.
(Ans. 80 %)
4. Rule of thumb. Using the oxygen scale,
can you develop a rule of thumb rela- 2. Find the excess air when firing no. 6 fuel oil
181